a) Field of the Invention
The invention is directed to a magnetic field sensitive sensor whose output signal with speed-independent amplitude yields information about the distance, rotational velocity (speed) and direction of rotation of a magnetic field simultaneously.
b) Description of the Related Art
Magnetic sensors with speed-independent output voltage in use heretofore rely on the large Barkhausen effect (English-language abbreviation: LBE). The LBE is a pulse-like complete magnetic reversal of special magnetic materials which have a privileged or preferred orientation of magnetic domains due to their composition and method of production. Since two stable states exist for the preferred orientation of the magnetic domains, structural component parts made from LBE materials are also known as bistable magnetic elements (hereinafter abbreviated as BME).
The magnetic reversal takes place within a time frame of roughly 50 .mu.s resulting in a limit frequency for the LBE of f.sub.Gr.apprxeq.20 kHz. Above f.sub.Gr, sensors in use heretofore do not generate a usable signal.
Since the magnetic reversal in LBE materials always takes place in a pulse-like manner when an external magnetic field has a frequency f less than f.sub.Gr, this effect is suitable for use in magnetic sensors. Previously used sensors with LBE materials can be divided into two classes: sensors without a magnetic exciting field and sensors with a magnetic exciting field.
Sensors without a magnetic exciting field are also known as pulse wire sensors (DE 3729949, DE 4107847, DE 3824075, DE 3406871). Devices for measuring velocity (DE 9014753, DE 3112709) can be realized by coupling pulse wire sensors with evaluating electronics. Patents have been applied for in a large number of sensors and devices in which LBE is combined with other physical operating principles (DE 3817704, DE 3008581, DE 3008582, DE 3046804, DE 3008526, DE 3008527, DE 3008560, DE 3008561, DE 3008562, DE 3008581, DE 3008582, DE 3008583, DE 3225499, DE 3225500, DE 342419, DE 3427582, DE 3637320, DE 3538514). However, all of the patented solutions have in common that they rely on the complete course of the LBE, i.e., complete magnetic reversal, and are capable of use only up to the limit frequency f.sub.Gr of the LBE.
In sensors with a magnetic exciting field, a constant magnetic reversal of the BME is carried out by the magnetic field of an exciting coil with exciting frequency f.sub.Err, wherein the condition for the occurrence of the LBE f.sub.Err &lt;f.sub.Gr must be met again for the exciting frequency. Sensors with a magnetic exciting field contain a sensor coil. The voltage U.sub.s induced in this sensor coil has voltage peaks due to the magnetic reversal of the BME in every half-wave. Depending on the orientation of the external magnetic field, the voltage peaks in every half-wave of the sensor signal can either be strengthened or weakened by an external magnetic field. The working point of the sensors can be adjusted by means of superposing a constant magnetic field on a working point coil (DE 3241018, DE 3718857, DE 4037052, DE 421358).
The magnetic resonance sensor differs in its function from other magnetic field sensitive sensors which likewise employ an oscillatory circuit (DE 8227446, DE 8316996, DE 8517733, DE 9010779, DE 9412765) through the use of a BME as a core of the sensor coil and the possibility of measuring speed, rotating direction and distance of the magnetic field from sensor simultaneously.